1. Field of the Invention
This invention relates generally to fire detectors of the ionization type that employ an ionization chamber for detecting products of combustion, and more particularly to supervisory circuits for such detectors which assure that the detectors are operating properly.
2. Prior Art
In order to provide maximum fire protection, it is desirable to monitor the operation of the fire protection device to assure that the device is receiving power and that the unit is otherwise operating properly.
Several systems for monitoring the power supplied to a fire protection device are known. These systems generally monitor the voltage of the power supply of the unit and compare the voltage thereof with a reference voltage obtained from, for example, a separate reference battery or reference voltage source, such as a zener diode.
Whereas these techniques provide a way to monitor the power supplied to a fire protection unit, in systems using a reference battery, such as described in U.S. Pat. No. 3,594,751, failure of the reference battery would render the monitoring circuit inoperative. In systems using a zener diode reference, a complete sudden failure of the main power supply would not be detected. Furthermore, the prior art circuits only detect malfunctions in the power supply, not in the detector circuitry itself.